The present invention relates to a support for a natural human heart which may be used for the surgical correction of a deformed heart valve, specifically a heart valve which has become dilated. In particular, the present invention relates to an annuloplasty ring prosthesis for implantation about heart valves.
The human heart generally includes four valves. Of these valves the more critical ones are known as the mitral valve, which is located in the left atrioventricular opening, and the tricuspid valve, which is located in the right atrioventricular opening. Both of these valves are intended to prevent regurgitation of blood from the ventricle into the atrium when the ventricle contracts. In preventing blood regurgitation both valves must be able to withstand considerable back pressure as the ventricle contracts. The valve cusps are anchored to the muscular wall of the heart by delicate but strong fibrous cords in order to support the cusps during ventricular contraction. Furthermore, the geometry of the heart valves ensure that the cusps over lay each other to assist in controlling the regurgitation of the blood during ventricular contraction.
Diseases and certain natural defects to heart valves can impair the functioning of the cusps in preventing regurgitation. For example, certain diseases cause the dilation of the heart valve annulus. Dilation may also cause deformation of the valve geometry or shape displacing one or more of the valve cusps from the center of the valve. Other diseases or natural heart valve defects result in deformation of the valve annulus with little or no dilation. Dilation and/or deformation result in the displacement of the cusps away from the center of the valve. This results in an ineffective closure of the valve during ventricular contraction, which results in the regurgitation or leakage of blood during ventricle contraction. For example, diseases such as rheumatic fever or bacterial inflammations of the heart tissue can cause distortion or dilation of the valvular annulus. Other diseases or malformations result in the distortion of the cusps, which will also lead to ineffective closure of the valve.
One method of repairing an impaired valve is to completely replace the valve. This method is particularly suitable for replacing a heart valve when one of the cusps has been severely damaged or deformed. However, presently available artificial heart valves are not as durable as natural heart valves, and it is usually more preferable if the patient's heart valve can be left intact.
While it is difficult to retain a heart having diseased or deformed cusps, the ability to surgically correct the deformation of the valve annulus at least provides the possibility of retaining the patient's valve intact. That is, while the replacement of the entire valve eliminates the immediate problem associated with a dilated valve annulus, presently available heart valves do not possess the same durability as natural heart valves. It is thus desirable to save the valve instead of performing a complete replacement.
Techniques have been developed to repair the shape of the dilated or elongated valve. These techniques, known as annuloplasty, is a surgical procedure of restricting the dilation of the valve annulus. Typically, a prosthesis is sutured about the base of the valve leaflets to restrict the dilation of the valve annulus. The prosthesis restricts the movement of the valve annulus during the opening and closing of the valve. The general desire in designing a prosthesis is to provide sufficient rigidity to ensure an adequate support of the valve annulus to allow for the possible healing of the valve annulus, while allowing for as close as possible the natural movement of the valve annulus during the opening and closing of the valve. This is particularly important since such prostheses are not normally removed from the heart valve, even if the valve annulus heals to a normal geometry.
Over the years different types of prostheses have been developed for use in annuloplasty surgery. In general prostheses are annular or partially annular shaped members which fit about the base of the valve annulus against the leaflets. Initially the prostheses were designed as rigid frame members, to correct the dilation and reshape the valve annulus to the natural state. These annular prostheses were formed from a metallic or other rigid material, which flexes little, if at all, during the normal opening and closing of the valve. Examples of rigid annuloplasty ring prostheses are disclosed in U.S. Pat. Nos. 3,656,185, issued to Carpentier on Apr. 18, 1972; and 4,164,046, issued to Cooley on Aug. 14, 1979. Certain artificial heart valves have also been developed with rigid frame members similar to the rigidity of the described valve prosthesis. An example of this type of heart valve are disclosed in U.S. Pat. Nos. 4,204,283, issued to Bellhouse et al on May 27, 1980; and 4,306,319, issued to Kaster on Dec. 22, 1981.
As stated, rigid annuloplasty ring prostheses adequately promote the healing of the valve annulus by restricting valve dilation and reshaping the valve annulus. However, this rigidity prevents the normal flexibility of the valve annulus. That is, a normal heart valve annulus continuously flexes during the cardiac cycle, and a rigid ring prosthesis interferes with this movement. Since it is standard to retain the prosthesis, even after the valve annulus has healed, the rigidity of the prothesis will permanently impair the functioning of the valve and the associated ventricle. Another disadvantage with a rigid ring prosthesis is the tendency for the sutures to become torn loose during the normal movement of the valve annulus.
Other workers have suggested the use of completely flexible annuloplasty ring prostheses, in order to overcome the disadvantages of rigid ring prostheses. This type of prosthesis is formed with a cloth or other very flexible material frame member. The resulting prosthesis provides little, if any resistance to the dilation of the annulus during the opening and closing of the valve. Furthermore, while these types of annuloplasty ring prothesis offer increased flexibility, such prosthesis fail to correct that valve disfunction due to the deformation of the valve annulus.
A further disadvantage with completely flexible ring prostheses is that the circumference of the ring is not fixed. That is, as the prothesis is being sutured to the annulus using, what are known as mattress sutures, the body of the prosthesis may become bunched at localized areas. This bunching of the prosthesis is generally referred to as multiple plications of the ring prosthesis. The resulting sutured prosthesis will not provide the desired reshaping of the valve annulus.
Examples of completely flexible ring prostheses are disclosed in U.S. Pat. No. 4,290,151, issued to Massana on Sept. 22, 1981, and are discussed in the articles of Carlos D. Duran and Jose Luis M. Ubago, "Clinical and Hemodymanic Performance of a Totally Flexible Prosthetic Ring for Atrioventricular Valve Reconstruction", 5 Annals of Thoracic Surgery, (No. 5), 458-463, (November 1976) and M. Puig Massana et al, "Conservative Surgery of the Mitral Valve Annuloplasty on a New Adjustable Ring", Cardiovascular Surgery 1980, 30-37, (1981).
Still further types of annuloplasty ring prostheses are designed to allow for adjustment of the ring circumference, either during the surgical implantation, or as the ring prosthesis during the opening and closing of the valve. This type of adjustable prosthesis is typically designed in combination with a rigid, or at least partially rigid frame member. For example, the ring prosthesis taught in U.S. Pat. No. 4,489,446, issued to Reed on Dec. 25, 1984, allows for self adjustment of the prosthesis annulus by constructing the valve frame member in two reciprocating pieces. However, while the resulting prosthesis is adjustable in at least one direction, the individual frame members are formed from a rigid material and thus the prosthesis suffers the same disadvantages with the rigid ring prosthesis discussed above.
Other examples of adjustable ring prostheses are taught in U.S. Pat. No. 4,602,911, issued to Ahmadi et al and 4,042,979, issued to Angell on Aug. 23, 1977, provide for mechanism of adjusting the ring circumference. In Ahmadi et al the ring prosthesis frame is a coiled spring ribbon which is adjusted by a mechanical screw assembly. In Angell, a drawstring is used to adjust the circumference of a rigid frame member. Again, these ring prostheses suffer from the disadvantages of the rigid ring prosthesis discussed above. The Angell prosthesis could also possess a substantially flexible portion after suturing which could include multiple plications for the reasons discussed above for the completely flexible prosthesis.
A further disadvantage with the Angell prosthesis relates to the design of the adjusting mechanism. The Angell prosthesis includes a rigid partial annular member. The open end of this member forms a gap which can be narrowed by tightening the drawstring. The tighter the drawstring is pulled the narrower the gap. The stress applied to the ring prostheses during the opening and closing of the valve is primarily directed to the drawstring. Thus failure of the drawstring allows the prosthesis annulus to expand, allowing the valve to dilate.
It would thus be advantageous to design an annuloplasty ring prosthesis having selective flexibility more closely resembling the naturally flexibility of the valve annulus to allow for a more natural movement of the valve during the cardiac cycle, while possessing selected areas of rigidity to allow for the reshaping of the valve. This annuloplasty ring prosthesis should also be formed from a substantially stiff body element to minimize the potential of forming multiple plications about the circumference of the prosthesis during the suturing procedure.
An annuloplasty ring prosthesis which partially achieved these results was taught in U.S. Pat. No. 4,055,861, issued to Carpentier on Nov. 1, 1977. The support taught and disclosed is described as being deformable, to an equal degree and simultaneously in all directions within and outside its resting plane, so as to form a skew curve. The preferred support is described as having the elasticity of an annular bundle of 2 to 8 turns of a cylindrical bristle of poly(ethylene terephthalate). In describing the support the individual bristles may either be interwoven, or merely arranged in a side by side relationship.
The extremities of the individual bristles are joined together to prevent the ends from sticking out through the outer cloth sheath by welding, gluing or ligature. It is thus apparent that the overall ring prosthesis will have a single flexibility. This flexibility will be dependent upon the flexibility of the individual bristles, and/or the number of these individual bristles used to construct the support.
While the device taught and disclosed in Carpentier '861 attempts to achieve flexibility in all planes, the resulting device may have a frame member either rigid or equivalent to the discussed completely flexible ring prosthesis, in either case such a ring prosthesis would have the disadvantages associated with such types of ring prostheses.
Furthermore, a ring prosthesis designed in accordance with Carpentier would suffer disadvantages from the excessive wear of the bristles rubbing against each other. This wear would cause flexural fatigue of the structure during normal activity of the valve. The ring prosthesis could also suffer from fatigue due to the differential application of the stress forces applied to the separate bristles or bristle windings. That is, during the natural movement of the valve the normal stress applied to the ring prosthesis would not be equally applied to each of the bristle strands or windings. This could result is fatigue of some of the bristle strands or windings severely affecting the functioning of the ring prosthesis.
It would thus be desirable to provide a ring prothesis which provides for a more natural flexibility of the valve annulus without suffering the above discussed disadvantages.